Changes in femoral posterior condylar offset and knee flexion after PCL-substituting total knee arthroplasty: comparison of anterior and posterior referencing systems

Anatomic Referencing Restores the Anatomy of the Distal Femur with Less Compromise

Historically, anterior referencing and posterior referencing are two specific techniques that surgeons can use for proper sizing of the femoral component in total knee arthroplasty (TKA). In this review, we introduce the concept of "anatomic referencing" which has become useful with more incremental sizes of the femoral component to more perfectly match the native anatomy of each patient and reduce overstuffing of the patellofemoral joint and medial-lateral (ML) overhang. Fifty consecutive TKA cases were reviewed where the novel anatomic referencing technique was used. Lateral radiographic projections were obtained preoperatively and postoperatively. The posterior condylar offset (PCO) was evaluated on the lateral radiographs by measuring the distance between the tangent line of the femoral diaphysis posterior cortex and the posterior condylar margin. PCO ratio (PCOR) was calculated by dividing the PCO by the distance between the posterior condylar border and a tangent line along the anterior cortex of the femoral diaphysis. Forty-five patients (50 TKAs) were reviewed. Average age of the patients was 70.34, range: 47-91. There were 19 males and 26 females reviewed in this series. On average, the delta PCOR was 0.022 (standard deviation = 0.032; min: -0.049, max: 0.082). When grouping our results into three main groups: < -0.03, -0.03 to 0.03, and > 0.03, we found that 62% fell within the -0.03 to 0.03 range. There was no statistically significant difference in delta PCOR between standard and narrow implants (p = 0.418). The proposed novel anatomic referencing technique has allowed for proper sizing of patients' femurs in the anteroposterior and ML direction while avoiding component overhang or the need for component downsizing to obtain a proper ML fit. This radiographic review confirmed this to be a highly accurate and reproducible technique.

Does referencing system affect the selection of implant size, position and gap balance in total knee arthroplasty?

BACKGROUND

(1) To evaluate if referencing system affects selection of implant size, position, and gap balance in total knee arthroplasty (TKA) with the use of contemporary implant designs and (2) to describe the authors' intraoperative sizing strategy using anterior referencing (AR) and posterior referencing (PR) systems.

METHODS

This was a retrospective review of 270 consecutive patients (397 knees) who underwent primary TKA with an AR or PR system. Selection of implant size, mediolateral and anteroposterior alignment of the femoral component, as well as gaps were compared between groups.

RESULTS

In the AR group, more patients had femoral components which were upsized or downsized compared to those in the PR group (29.5% vs 12.0% respectively) and in patients who underwent bilateral TKA, 49.4% of those in the AR group had femur component size asymmetry. The AR group had better medio-lateral (ML) fit over the distal cutting surface area, smaller change in anterior offset but higher incidence of anterior notching when compared to the PR group. Posterior condylar offset (PCO) was restored in both groups and gap differences in flexion-extension and ML were comparable. There was also no difference in clinical scores and ROM between groups at 2-years follow-up.

CONCLUSION

In this study, conventional implications related to referencing system were not observed. In practice, AR systems can restore PCO while PR systems do not result in increased anterior notching or anterior overstuffing. Differences observed in this study are most likely related to implant design specifics and surgical technique.

Which is better? Anterior or posterior referencing for femoral component position in total knee arthroplasty

When sizing the femoral component or determining its placement in total knee arthroplasty (TKA), if the anterior-posterior diameter of the femoral condyle is between component sizes, the selected size will differ depending on whether anterior referencing (AR) or posterior referencing (PR) is used. As a result, the amount of resected bone will also vary. In the present prospective study, we compared the two referencing methods to determine which is more suitable for individual patients. We recruited 58 patients (92 joints) who received TKA using the standard technique with intermediate-size components. AR was used in 26 joints, and PR in 23 joints. Seventeen of the patients underwent same-day bilateral TKA in which components of different sizes were used for the left and right joints. AR resulted in significantly smaller anterior and posterior offsets than PR. Preoperative clinical evaluation revealed no significant differences among cases in which intermediate-size components were indicated, or those in which components of different sizes were indicated. When an intermediate-sized component was indicated using the AR method, moving the sizer forward resulted in a larger posterior gap, but this technique was nevertheless considered acceptable. AR is likely to be more suitable than PR as it achieves more physiological anterior clearance.

Three-year clinical and radiological results of a cruciate-retaining type of the knee prosthesis with anatomical geometry developed in Japan

Background

The FINE total knee was developed in Japan and clinical use began in 2001. It has unique design features, including an oblique 3^o femorotibial joint line that reproduces anatomical geometry. Although 20 years have passed since the FINE knee was clinically used for the first time in Japan, a formal clinical evaluation including patient-reported and radiographic outcomes has not been undertaken.

Methods

A total of 175 consecutive primary cruciate-retaining (CR)-FINE total knee arthroplasties (TKAs) at our hospital between February 2015 and March 2017 were included in this study. Three years postoperatively, range of motion (ROM), Knee Society Score (KSS), Knee Injury and Osteoarthritis Outcome Score (KOOS) and Forgotten Joint Score (FJS) were recorded and compared with preoperative scores. Radiographic analyses including mechanical alignment, component alignment, and incidence of radiolucent lines also were undertaken based on the radiographs 3 years postoperatively.

Results

One-hundred twenty-two knees (70%) were available for 3-year follow-up data using KOOS, except for the sports subscale. Postoperative KOOS-symptom, −pain and -ADL were > 85 points, but KOOS-sports, −QOL and FJS were less satisfactory. ROM, KSS and all the subscales of KOOS were significantly improved compared with preoperative scores. Postoperative mean FJS was 66 and was significantly correlated with all the subscales of KOOS, but not with postoperative ROM. Radiolucent lines ≧1 mm wide were detected in five knees (4.1%). There were no major complications needing revision surgeries.

Conclusions

Patient-reported outcomes (PROs) for symptoms, pain and ADL after the CR-FINE TKA were generally improved, but those for sports, QOL and FJS were improved less. The incidence of radiolucent lines was rare but detected around the femoral components. With the mid- to long-term follow-up, improvements of surgical technique will be necessary to achieve better PROs from patients receiving the FINE knee.

Does increased femoral component size options reduce anterior femoral notching in total knee replacement?

OBJECTIVE

Total knee arthroplasty (TKA) is currently the best option for management of advanced knee arthritis for patients who have exhausted conservative management. There have been significant implant design improvements and this is a continuing process to help the surgeon replicate patient anatomy and kinematics. Amongst the many variables in implantation to achieve a well-functioning TKA, getting optimal femoral component sizing is one. Every implant system has certain discreet implant sizes and the surgeon has to strive to obtain the best fit possible for the patient and attain a well aligned and stable TKA. The aim of this study was to assess the frequency of various femoral component sizes being implanted with a system which has 2.5 mm antero-posterior increment between sizes, and to assess the incidence of anterior femoral notching when using a posterior referencing system.

MATERIALS AND METHODS

A retrospective analysis of 739 TKAs implanted in 532 patients between January 2013 and January 2016 at a single center using a single posterior stabilized implant system was done. Patient demographics and femur component size used was obtained from hospital patient records. Immediate post-operative radiographs were analyzed to look for anterior femoral notching and presence of this was classified according to Tayside classification. A telephonic follow up at minimum 2 tears post-surgery was done to interview for occurrence of supracondylar femur fracture or revision for any other causes.

RESULTS

There were 207 bilateral and 325 unilateral TKAs performed in 532 patients during the study period. There were 245 males and 287 females with an average age of 61.3 years (43-81 years, SD = 7.2). The most commonly used femoral component was 60 mm and an intermediate size prosthesis was used in 43.11% patients. The incidence of femoral notching ranged from 0 to 6.3%. No patient had sustained a supracondylar condylar fracture at minimum 2 years follow up.

CONCLUSION

The availability of a larger number of femoral components in a TKA system allows the surgeon the modularity to choose and obtain the best fit possible. Restoration of posterior condylar offset, preventing anterior notching, medio-lateral overhang and patellofemoral joint stuffing are greatly dependent on correct femoral component sizing. The findings from our study underscore the need to use an implant system with as many femoral size options as possible with lesser increments in between sizes to minimize anterior femoral notching when using a posterior referencing technique.

Posterior condylar offset changes and its effect on clinical outcomes after posterior-substituting, fixed-bearing total knee arthroplasty: anterior versus posterior referencing

Background

We sought to determine whether there was a difference in the posterior condylar offset (PCO), posterior condylar offset ratio (PCOR) and clinical outcomes following total knee arthroplasty (TKA) with anterior referencing (AR) or posterior referencing (PR) systems. We also assessed whether the PCO and PCOR changes, as well as patient factors were related to range of motion (ROM) in each referencing system.

Methods

This retrospective study included 130 consecutive patients (184 knees) with osteoarthritis who underwent primary posterior cruciate ligament (PCL)-substituting fixed-bearing TKA. The difference between preoperative and postoperative PCO and PCOR values were calculated. Clinical outcomes including ROM and Western Ontario and McMaster University (WOMAC) scores were evaluated. Furthermore, multiple linear regression analysis was performed to determine the factors related to postoperative ROM in each referencing system.

Results

The postoperative PCO was greater in the AR group (28.4 mm) than in the PR group (27.4 mm), whereas the PCO was more consistently preserved in the PR group. The mean postoperative ROM after TKA was greater in the AR group (129°) than in the PR group (122°), whereas improvement in WOMAC score did not differ between the two groups. Preoperative ROM was the only factor related to postoperative ROM in both groups.

Conclusions

There was no difference in postoperative PCO in AR and PR group and the PCO was not associated with postoperative ROM. PCO was more consistently preserved after surgery in the PR group. The postoperative PCO and PCOR changes did not affect the postoperative ROM. Furthermore, similar clinical outcomes were achieved in the AR and PR groups.

Trial registration

Retrospectively registered (Trial registration number: 06-2010-110).

Gender differences in morphology exist in posterior condylar offsets of the knee in Korean population

PURPOSE

This study aimed to analyze the morphometric data from magnetic resonance images of arthritic knees in Korean adults, and to identify the existence of morphological differences of femoral posterior condylar offset (PCO) between genders.

METHODS

The differences in anthropometric PCO data in 975 patients (825 female and 150 male) were evaluated. The distances from the anterior and posterior femoral shaft cortex line to the most posterior femoral condyle tangent line were defined as the anterior-posterior dimension (AP) and the PCO. The PCO ratio (PCOR) was calculated as PCO/AP.

RESULTS

The medial PCO was greater than the lateral PCO (26.3 ± 2.2 vs. 24.3 ± 2.3 mm, p < 0.01). This difference was observed in both female patients (medial: 26.2 ± 2.2 mm vs. lateral: 24.2 ± 2.2 mm, p < 0.01) and male patients (medial: 26.8 ± 2.3 mm vs. lateral: 24.8 ± 2.4 mm, p < 0.01). The medial and lateral PCO values were also greater in male patients than in female ones (p < 0.01). In contrast, PCOR was greater in female patients than in male ones, both in the medial and lateral femoral condyles (p < 0.01).

CONCLUSIONS

It was shown that medial and lateral PCO and PCOR were asymmetric, and that there was gender difference in Korean population in our study. In addition, our data showed that the PCOR of contemporary TKAs may be small for Asian patients that may not be sufficient to meet the needs of the Korean patient population. These results confirm that a gender-specific femoral component design is necessary to recreate the PCO for male and female Asian populations.

LEVEL OF EVIDENCE

Non-consecutive patients, Level III.

Posterior Reference Position Affects Intraoperative Kinematic and Soft Tissue Balance in Navigated Posterior-Stabilized Total Knee Arthroplasty

BACKGROUND

The importance of medial compartment stability is recognized in total knee arthroplasty (TKA). To manage the medial extension-flexion gap, the posterior reference position can be changed from conventional posterior center to posterior medial in measured resection techniques. This study aimed to compare the intraoperative soft tissue balance and rotational kinematics between the posterior medial and posterior center reference groups.

METHODS

We enrolled 57 consecutive patients with varus osteoarthritis undergoing posterior-stabilized (PS) TKA using an image-free navigation system. The detailed surgical plan in both groups and intraoperative kinematics were recorded using navigation, and soft tissue balance measured with an offset-type tensor was statistically compared between groups.

RESULTS

Patients were divided into the posterior center reference group (n = 32) and posterior medial reference group (n = 25). The posterior medial and posterior lateral condyles were significantly thicker in the posterior center reference group (P < .05). Although preoperative rotational kinematics were comparable between groups, the tibial rotational position was significantly more externally rotated in the posterior center reference group than in the posterior medial reference group at 45°, 60°, and 90° of flexion (P < .05). The varus angle and joint component gap were significantly smaller in the posterior medial reference group than in the posterior center reference group at 60° and 90° of flexion (P < .05).

CONCLUSION

The posterior reference position affects intraoperative kinematics and soft tissue balance in navigated PS TKA. Posterior medial reference PS TKA decreases the excessive tibial external rotation during midflexion and increases the flexion stability compared with conventional posterior center reference PS TKA.

Effect of the Referencing System on the Posterior Condylar Offset and Anterior Flange-Bone Contact in Posterior Cruciate-Substituting Total Knee Arthroplasty

BACKGROUND

The effect of referencing system on posterior condylar offset (PCO) after total knee arthroplasty (TKA) is still controversial. Moreover, there is a lack of concern about the anterior flange-bone contact according to the referencing system.

METHODS

One hundred four TKAs using the anterior referencing (AR) system and 107 TKAs using the posterior referencing (PR) system were analyzed with 2-year follow-up. The PCO, PCO ratio (PCOR), and contact at the anterior flange-bone interface were compared between the 2 groups. The flexion and extension gaps and the degree of medial release were measured, and clinical outcomes were evaluated. Finally, the correlation between changes in PCO and knee flexion angle was analyzed.

RESULTS

The mean postoperative PCO and PCOR were significantly larger in the PR group than in the AR group. Incomplete contact between the anterior flange and anterior femur occurred more frequently in the AR group than in the PR group (48.1% vs 13.1%, P < .001). The medial and lateral flexion gaps were significantly larger in the AR group than in the PR group. The groups showed no differences in soft tissue release, degree of flexion, and clinical scores. In both groups, there was no correlation between postoperative change of PCO and improvement in flexion.

CONCLUSION

The PR system produced larger PCO and PCOR, and smaller flexion gap compared to the AR system. Additionally, the PR group showed more favorable contact between the anterior flange and anterior femur. However, these differences were not related to the degree of soft tissue release and clinical outcomes.

Interactive effect of femoral posterior condylar offset and tibial posterior slope on knee flexion in posterior cruciate ligament-substituting total knee arthroplasty

BACKGROUND

This work aimed to evaluate the changes in the femoral posterior condylar offset (PCO) and tibial slope after posterior cruciate ligament (PCL)-substituting total knee arthroplasty (TKA), and to address the presence of any interactive effect between the two on knee flexion.

METHODS

Fifty-two PCL-substituting TKAs were performed using a posterior referencing system. Three-dimensional reconstructed computed tomographic (CT) images were used to evaluate PCO and tibial slope before and after arthroplasty. Range of motion and clinical scores were evaluated at a mean of 3.1years postoperatively. Multivariate linear model with interaction terms was used to evaluate and compare the relationships among changes in PCO, tibial slope, and postoperative knee flexion angles.

RESULTS

The degree of change in PCO was greater in the lateral condyle than in the medial condyle (3.1±2.5mm and -0.5±2.8mm, respectively). Postoperative medial and lateral tibial slopes were 1.4°±1.8 and 1.4°±2.0, respectively. The mean degree of postoperative knee flexion was 125°. Analysis with interaction terms and covariate adjustment demonstrated that medial PCO and tibial slope were significantly related to knee flexion with interactive effect (P=0.011). In cases with <3° posterior tibial slope, the postoperative PCO was positively correlated to the degree of knee flexion angle. However, in cases with >3° tibial slope, PCO was negatively correlated to knee flexion.

CONCLUSION

Medial femoral PCO and tibial slope showed interactive effect on knee flexion after PCL-substituting TKAs. Reconstitution of the proper PCO and avoiding excessive tibial slope may be necessary.